PHOTOSYNTHESIS IN COFFEE (COFFEA-ARABICA AND C-CANEPHORA) AS AFFECTEDBY WINTER AND SUMMER CONDITIONS

Photosynthetic and biochemical responses of potted plants of Coffea ar abica cv Red Catuai and C. canephora cv Kouillou were examined during winter and summer. There were large decreases in the photosynthetic ra tes of both cultivars from summer to winter, with more pronounced decl ines shown by Catuai. The photochemical efficiency of photosystem II, as evaluated by the ratio of variable to maximum chlorophyll fluoresce nce, decreased to a greater extent in Catuai than in Kouillou during w inter. This probably was a secondary effect due to the loss of the pho tosynthetic capacity, which was mostly determined by non-stomatal fact ors. In response to winter conditions, Kouillou accumulated three time s more proline and ascorbate with no changes in the content of maloned ialdehyde (MDA). Catuai accumulated 160% more proline and 206% more MD A in winter in comparison to summer values, but there was no significa nt change in ascorbate levels. The content of chlorophylls and caroten oids did not change in response to natural seasonal acclimation. The l eaf starch content in winter was higher by 53% in Catuai than in Kouil lou. Photosynthetic rates, as measured by oxygen evolution, were well correlated with starch content in Catuai, but not in Kouillou. When wi nter-grown leaves were darkened for 96 h, their normal starch levels w ere halved: this was accompanied by the restoration of the photosynthe tic rates to levels similar to those found in summer in both cultivars , with a concurrent resumption of the photosystem II efficiency. (C) 1 997 Elsevier Science Ireland Ltd.